package edu.hz.pro1_50;

import java.util.Scanner;

public class Main1001 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNext()) {
            int n = scanner.nextInt();
            int sum = 0;
            for (int a = 1; a <= n; a++) {
                sum += a;
            }
            System.out.println(sum);
            System.out.println();
        }
    }
}
